If you want authentic Advent parts, try eBay. Just make sure you look very carefully at the photos, ask the seller all the right questions, and buy from sellers with very high percentage feedback ratings - and look for sellers who are into hifi, rather than sellers who are just flipping things they found at a flea market or in someone's closet. In some cases it might make sense to buy an entire speaker to salvage the parts, but one way or another there should be plenty of parts for most Advent speakers. I'd avoid refoamed and re-surrounded woofers if possible; look for authentic, original, excellent condition parts and ask the seller if they are the original owner or if they know the item's ownership history - and if the item has always been stored in a normal (temperature and humidity controlled) environment, etc.
This hobby takes work, but it can be done :)
Good luck.
